Wavefront reconstruction with pupil fragmentation

What is it about?

The use of smaller subapertures on some recent adaptive optics (AO) systems seems to yield difficulties in wavefront reconstruction, known as spider effect or pupil fragmentation: the size of the subapertures is small enough so that some of them are masked by the telescope spider, dividing the pupil into disconnected domains. In particular, this problem will arise on the E-ELT. We have studied pure wavefront reconstruction on a Shack-Hartmann wavefront sensor, for a simplified AO system similar to VLT/SPHERE in size, with and without pupil fragmentation, and compared the performance of various wavefront reconstructors for different signal-to-noise ratios, using priors (minimum variance) or not (least-squares), and with different assumptions for the damaged wavefront measurements.

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